The present invention relates to a method of and an apparatus for coiling a metal strip when coiling on a mandrel the metal strip rolled at high speed like in a hot rolling and, in particular, relates to a method of and an apparatus for coiling a metal strip, each of which is adapted such that wrapper rolls are pushed against an outer coiling face of coil before a coiling is finished to thereby brake a rotation of the coil and, by this, the rotation of the coil is stopped in a short time when the coiling is finished.
In a hot rolling line, a hot-rolled metal strip is coiled by a coiler disposed in a downstream side of a finishing mill, thereby making a coil. Hitherto, if one material to be rolled is finish-rolled, the rolled material to be rolled is coiled by the coiler as one coil. As to an unsteady portion such as tip portion or tail portion of the material to be rolled, a shape control or a meander control of the material to be rolled is difficult. Further, recently, it is desired to thin the hot-rolled metal strip, but if a thickness of the rolled metal strip becomes thin, the shape control or the meander control becomes more difficult. Therefore, by means of increasing a weight rolled in a finishing roll in one time by increasing a weight of one material to be rolled or connecting a preceding material to be rolled and a following material to be rolled in an inlet side of the finishing mill, it is performed to make a rate occupied by the unsteady portion small.
In this case, since there is a limit in the weight capable of being coiled by the coiler in one time, plural coilers are disposed, a strip shear is provided between the finishing mill and the coilers, the metal strip sent out from the hot finishing mill is cut in a predetermined length by the strip shear and, thereafter, it is coiled alternately by the plural coiling devices in a coil-like form. On this occasion, in order to shorten a time until the coiling of the metal strip by the next coiling device is started, it is necessary to stop the rotation of the coil in a short time as far as possible after the coiling of the metal strip by the present coiling device has finished.
As an apparatus for coiling a metal strip, which responds to such a demand, there is disclosed one described in Japanese Patent Laid-Open No.154550/1993 Gazette for instance. This apparatus for coiling a metal strip is one which is, as shown in FIG. 6, adapted such that plural wrapper rolls 6 are arranged so as to be able to approach or separate from an outer coiling face of a coil 5, the wrapper rolls 6 are approached toward the outer coiling face of the coil 5 to thereby apply a predetermined pushing force to the outer coiling face before finishing the coiling and, by this, a flutter of tail end of the coil 5 is prevented and the rotation of the coil 5 is stopped in a short time by being braked when finishing the coiling. Further, when starting the coiling, the wrapper rolls 6 are disposed adjacently to a mandrel 2 of a coiling device 1 to thereby sandwich a tip of the metal strip between them and the mandrel 2 and, by this, have in combination also a function of surely performing a coiling start operation. Incidentally, it is adapted such that, after the coiling has been started, the wrapper rolls 6 are disposed separating from the outer coiling face of the coil 5 until a predetermined time before the coiling is finished.
By the way, for example, in the aforesaid hot rolling method in which the preceding material to be rolled and the following material to be rolled are connected in the inlet side of the finishing mill, it is made possible to perform a thin material rolling by applying a stable tension over a whole length by means of continuously rolling one in which several to several tens rolling raw materials are connected.
However, in case that a thin metal strip is coiled at high speed by using the aforesaid conventional apparatus for coiling a metal strip, as shown in FIG. 7, when the outer coiling face of the coil 5 is pushed by the wrapper roll 6, if the wrapper roll 6 impinges against a portion located in a step between an inner coiling most tip portion (metal strip tip) 5a of the coil 5 in an outer coiling face of the coil 5 and a surface of the mandrel 2 (hereafter, referred to as step portion 16), the step portion 16 is rolled by a high pressure because the coil 5 is rotating at high speed. As a result, there is a disadvantage that a portion, of the metal strip being coiled, located at the step portion 16 generates a shape defect, so that a yield is deteriorated. And, it has been confirmed that this shape defect becomes remarkable in case that a thickness is 2.3 mm or less and a coiling speed is 700 mpm or higher. Incidentally, it is frequent that the wrapper roll 6 is provided with a convex crown, so that the aforesaid shape defect is mainly a center buckle.
Further, in ones described in Japanese Patent Laid-Open No. 126021/1981 Gazette and Japanese Patent Laid-Open No. 92118/1984 Gazette, there is disclosed a method of buffering an impact force generated in the step portion by, in a machine for coiling a metal strip, performing an operation for raising at a coil step portion generated in a metal strip tip portion before an upper roll passes in an initial stage of coiling the metal strip on a mandrel to thereby avoid an impingement and for lowering the upper roll after it has passed. However, since such a case as mentioned before in which the weight of one material to be rolled is large and the fact the one in which several to several tens rolling raw materials are connected is continuously rolled and coiled at high speed are not assumed, there is not disclosed the fact that, when finishing the coiling, it is stopped in a short time by means of braking a rotation of the coil by the plural wrapper rolls. Accordingly, in case that a continuous finish-rolling is performed or in case that a large unit weight coil is rolled, since a high speed winding is performed, there is a disadvantage that, in case that there is the step in a coil outer coiling portion, the step portion is rolled by a high pressure, so that this portion generates the shape defect.
The invention has been made in order to solve such a disadvantage, and its object is to provide a method of and an apparatus for coiling a metal strip, each of which can intend an improvement in yield by adapting such that the shape defect is not generated when coiling a thin metal strip at high speed.
In order to achieve such an object, the invention 1 is a method of coiling a metal strip, adapted such that, before the metal strip after a hot finish rolling is finished to be coiled on a mandrel, plural wrapper rolls are pushed against an outer coiling face of a coil to brake a rotation of the coil, thereby stopping the rotation of the coil, characterized in that a position of a step portion appearing in an outer coiling face of the coil owing to a step between an inner coiling most tip portion of the coil and a surface of the mandrel is detected, and a pushing force per a coil width 1m of the wrapper roll is made 20 kN/m or lower only during a predetermined time before and after the step portion passes a position of the wrapper roll.
A method of coiling a metal strip according to the invention 2 is characterized in that, in the invention 1, the wrapper roll is separated from the outer coiling face of the coil only during the predetermined time before and after the step portion passes the position of the wrapper roll.
A method of coiling a metal strip according to the invention 3 is characterized in that, in the invention 1, the pushing force per a coil width 1 m of the wrapper roll at the step portion and a portion other than the step portion is made 10-20 kN/m.
A method of coiling a metal strip according to the invention 4 is characterized in that, in the inventions 1-3, before the metal strip is finished to be coiled on the mandrel, the wrapper roll is approached from a waiting position nearer to the mandrel than an open limit toward the outer coiling face of the coil, thereby starting a pushing of the outer coiling face.
The invention 5 is an apparatus for coiling a metal strip, having a mandrel for coiling the metal strip in a coil-like form, plural wrapper rolls for pushing an outer coiling face of a coil coiled on the mandrel, a support frame which supports the wrapper roll and which is provided so as to be able to approach or separate from the outer coiling face of the coil, and drive means for causing the support frame to approach or separate from the outer coiling face of the coil, characterized by having strip shear controlling means for transmitting a coiling finish signal to a strip shear for cutting the metal strip after a hot finish rolling and to drive means for pushing the wrapper roll against the outer coiling face of the coil, step portion position detecting means for detecting a position of a step portion appearing in the outer coiling face of the coil owing to a step between an inner coiling most tip portion of the coil and a surface of the mandrel, and wrapper roll controlling means for controlling, on the basis of a detection position by the step portion position detecting means, the drive means such that a gap between the wrapper roll and the outer coiling face or a pushing force of the outer coiling face by the wrapper roll is changed.
An apparatus for coiling a metal strip according to the invention 6 is characterized in that, in the invention 5, the step portion position detecting means has means for detecting, when starting to coil the metal strip, a position of a tip of the metal strip coiled on the mandrel, means for operating the tip position as a rotation angle xcex8 with respect to a predetermined position of the mandrel, means for storing the xcex8, and means for operating, before the metal strip is finished to be coiled, the xcex8 as the position of the step portion appearing in the outer coiling face of the coil.
An apparatus for coiling a metal strip according to the invention 7 is characterized in that, in the invention 6, the xcex8 is found by a sensor for detecting the fact that the metal strip tip has passed, a rotation speedometer for detecting a rotating speed of the coil, and a sheet speed detecting sensor.
A method of coiling a metal strip according to the invention 8 is characterized in that, in the invention 1, in case that a rotating speed of the coil is reduced to lower than a predetermined rotating speed, the pushing force of the wrapper roll is set so as to exceed 20 kN/m.